1. Field
The present disclosure relates to a light emitting device and a method of manufacturing the light emitting device, and more particularly, to an organic light emitting device (OLED), which has an improved extraction efficiency by using a transparent electrode composed of two or more layers with different refractive indices, and a method of manufacturing the OLED.
2. Description of the Related Art
An OLED, unlike for example, a light emitting diode (LED) which is a point light source composed of a compound semiconductor material, is capable of performing surface light emission, and has many advantages such as low power consumption, high outdoor visibility, flexibility, and so forth. For this reason, the OLED has attracted much attention from an illumination field as well as a display device field. However, the OLED typically has a low light extraction efficiency such that only about 20% of emitted light is emitted to outside. The low light extraction efficiency mainly originates from a refractive index difference between an organic light emission layer and the external air. That is, only light in a region of a predetermined angle from light generated in an organic light emission layer is emitted to the outside, and light in the other-angle region disappears by being absorbed in the OLED due to total reflection occurring in an interface with the air.
To improve the light extraction efficiency of the OLED, light extraction layers having various structures have been used. For example, a light extraction layer in a micro-lens array form may be attached onto an external surface of a substrate. However, the external light extraction layer formed on the external surface of the substrate does not prevent light loss occurring between layers in the OLED, thus having a limitation in efficiency improvement.
Therefore, various structures for implementing the light extraction layer in the OLED have been proposed. For example, such an internal light extraction layer is generally disposed between a substrate and a transparent electrode. The internal light extraction layer typically includes unevenness or a scatterer, which may degrade surface flatness of a transparent electrode. If the surface flatness of the transparent electrode degrades, electric charges such as holes and electrons are concentrated onto a particular region, degrading electric characteristics of the OLED.